This application claims the priority of German application No. 100 38 525.7, filed Aug. 8, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a catalyst element for a stacked reactor for generating hydrogen from hydrocarbons having a catalyst disc of porous material. This catalyst element is suitable for connecting a stacked reactor to the environment. The present invention also relates to a process for producing the catalyst element; to a stacked reactor which is constructed from a plurality of catalyst discs stacked on top of one another; and to a process for producing a stacked reactor.
German laid-open publication 197 43 673 A1, discloses a device for the generation of hydrogen which has at least one thin, large-area layer (catalyst disc) which is formed by compressing catalyst material and through which a reaction mixture can be forced. The reaction mixture loses pressure as it passes through the catalyst disc. The catalyst disc has a mesh-like support structure, which preferably consists of dendritic copper. This mesh-like support structure is created by admixing a metal powder comprising dendritic copper with a catalyst powder and compressing this mixture to form a shaped body, the catalyst disc in the green state. Then, the shaped body is sintered, and the catalyst disc is finished. A plurality of catalyst discs which have been stacked on top of one another and joined together form a stacked reactor.
German patent application 198 47 987.5 discloses a device for the generation of hydrogen comprising at least one thin, large-area catalyst layer (catalyst disc). The starting material for producing the catalyst disc is exclusively copper powder, i.e. no additional fraction of a catalytically active material is admixed with the copper powder. For its production, the copper powder, preferably dendritic copper, is pressed to form a shaped body in the form of a thin, highly compressed layer which will form the catalyst disc. The shaped body is then sintered in a reducing atmosphere, forming a xe2x80x9ccatalyst discxe2x80x9d without a catalyst layer. To form a thin, large-area catalyst layer, a surface layer of the shaped body is activated, as a catalyst layer, by repeatedly oxidizing and reducing the surface of the shaped body. A stacked reactor is constructed from a plurality of catalyst discs which have been stacked on top of one another and joined together.
German patent application 198 32 625.4 discloses a stacked reactor comprising catalyst discs stacked on top of one another and a process for producing a stacked reactor. In this case, catalyst discs in the green state, i.e. the pressed shaped bodies prior to the sintering process, are stacked on top of one another to form a stacked reactor and are then sintered jointly in the stacked state. The sintering may take place under the action of a predetermined pressure. The joint sintering results in a sealed connection between the individual catalyst discs.
Stacked reactors of this type are usually fitted in a housing and connected to connection lines, for example for starting material stream and product stream. The stacked reactors and the connections have to be securely sealed with respect to the outside. In the prior art, the sealing forces required are applied as compressive forces across the entire stacked reactor. For this purpose, it is necessary for the entire stacked reactor to be clamped in place by complex clamping devices. In operation, changes in spacing or expansion have to be absorbed by springs or similar compensation elements. Therefore, the clamping device has to be matched as accurately as possible to the dimensions of the stacked reactor, and it is difficult to install stacked reactors of different dimensions.
The present invention is based on the object of providing a catalyst element, in particular for the production of a stacked reactor of the type described in the introduction, which allows simple and inexpensive connection to the environment without connection forces which occur in the process acting on the catalyst element or on a stacked reactor of this type.
This object is achieved by a catalyst element according to the present invention. Furthermore, a stacked reactor for generating hydrogen from hydrocarbons may comprise at least one catalyst element according to the present invention as a catalyst connection disc.
The catalyst element according to the present invention for a stacked reactor for generating hydrogen from hydrocarbons, having a catalyst disc of porous material, includes a solid connection element. The catalyst-side end of the solid connection element is at least partially enclosed by the catalyst disc and is joined to the disc. Attachment means are provided at the exposed end of the connection element, which is remote from the catalyst. The solid connection element can be joined to the porous material of the catalyst disc by sintering, soldering, welding, adhesive bonding, screwing and/or clamping. Sintering is carried out under the application of pressure. In one embodiment, it is also possible for a mediator layer to be provided between the catalyst-side end of the connection element and the surface of the catalyst disc.
As noted, the catalyst-side end of the connection element may have a mediator layer. The mediator layer is joined to the connection element over the entire area by sintering, soldering or adhesive bonding. The mediator layer is joined to the catalyst disc over the entire area by sintering and attachment means are provided at the exposed end, which is remote from the catalyst, of the connection element. If the connection element used is produced from a different material from the mediator layer which follows, it is possible, in order to improve the adhesion between connection element and mediator layer, to provide a metal layer which is produced by electrodeposition. The layer thickness of this metal layer may usually be from approximately 50 xcexcm to a few 100 xcexcm. The mediator layer itself, which contains or consists of a metal or a metal alloy, has a layer thickness of approximately 0.5 to 3 mm, preferably of approximately 1 to 2 mm. By way of example, when using a connection element made from stainless steel and a mediator layer, preferably of dendritic copper, the metal layer produced by electrodeposition will also be copper.
The catalyst disc or a stacked reactor constructed therefrom is connected to the environment via the connection element and the attachment means. Connecting forces are therefore advantageously absorbed by the solid connection element and are not transmitted to the catalyst disc or the stacked reactor. It is not necessary to clamp the entire stacked reactor, and consequently it is possible to dispense with a complex clamping device.
Substantially only the forces from the weight of the catalyst disc/stacked reactor, and possibly acceleration forces depending on the selected mounting/attachment, act between the connection element and the catalyst disc. The fact that the solid connection element is at least partially embedded in the porous catalyst disc or that the connection element and catalyst disc are joined by a mediator layer means that the active connection forces (1) between catalyst disc and connection element and (2) between connection element and environment connection are separated from one another.
The following facts must be taken into account when joining the connection element and the catalyst disc:
The catalyst disc, preferably made from copper, containing catalyst material or a catalyst layer on the surface, is heat-sensitive. However, it can only be joined to the connection element, preferably of stainless steel, at elevated temperatures. To obtain a connection between catalyst disc and connection element, it is possible to achieve this by a clamping mechanism or via a mediator layer located between catalyst disc and connection element, in which case the different temperature compatibility of the components or materials has to be taken into account through two process steps. In a first step, the connection element is combined at high temperatures with the mediator layer, by soldering at approximately 800xc2x0 C. to 1000xc2x0 C.; by sintering at approximately 600xc2x0 C. to 1000xc2x0 C. under pressure; or by adhesive bonding using an adhesive which is suitable for the materials used. In a subsequent second step, the catalyst disc is attached to the mediator layer, advantageously at a lower temperature by sintering on under pressure at temperatures of approximately 400xc2x0 C. to 600xc2x0 C. The catalyst disc may also be constructed from different metals or metal alloys.
To join the connection element and catalyst disc or connection element and mediator layer, it is possible to use a soldering operation employing, for example, silver solder or material which contains silver solder.
In one configuration of the present invention, a projection, which extends substantially perpendicular to the expected principal direction of load on the connection between catalyst disc and connection element, is provided on the catalyst-side end of the connection element. Designing the catalyst-side end in this way assists with joining catalyst disc and connection element by providing a form fit in addition to the joining forces which are present according to the particular type of joining process selected.
In a preferred embodiment of the present invention, a surface region of the catalyst-side end of the connection element ends substantially flush with the outer surface of the catalyst disc, and a section of the catalyst-side end extends at least partially parallel to the outer surface of the catalyst disc. By way of example, it is possible to achieve such a design of the catalyst-side end by providing a step-like structure. When connecting/joining the catalyst disc, it is possible, by a corresponding mating surface which rests substantially flat against the catalyst top side and the surface region, to ensure that the connection between catalyst disc and connection element is additionally clamped and thereby reinforced. The mating surface may be produced, for example, by a plate or a suitably designed environment connection.
In a preferred configuration of the present invention, the connection element has at least one passage, via which reaction starting materials and/or reaction products of the catalyst or stacked reactor are supplied and/or discharged. By way of example, a catalyst or a stacked reactor can be connected to suitable supply connections from the environment via the passage in the connection element. The sealing forces required to provide a reliable seal of the connection are in this case absorbed by the connection element and do not act on the catalyst or stacked reactor.
It will be understood that the features which have been mentioned above and those which are yet to be explained below can be used not only in the combination given in each instance but also in other combinations or on their own without departing from the scope of the present invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.